Re: Migration to AL32UTF8 from WE8ISO8859P15

Luc

Yes, we changed every varchar2 column from BYTE to CHAR which I admit was probably overkill, it may be that the majority of columns will only ever contain ASCII characters. But that required some analysis by the application developers, so instead of having to rely on them we just did the sledge-hammer approach and did them all.

We did change the NLS_LENGTH_SEMANTICS to CHAR as well but be warned that you may have to change it back temporarily to BYTE when doing upgrades.

Also 1 point that I forgot to mention that you *must* modify the database characterset first before altering the columns otherwise you still get trunacated columns on import, at least that was our experience.

Cheers
Luke

Luc Demanche wrote:
> Luke,
>
> I forgot to ask you.
> So, you have change every vachar2 for CHAR. And after have you
> changed the database to use CHAR (NLS_LENGTH_SEMANTICS = CHAR) ?
>
> Thanks
> Luc
>
>
>
> On 1/11/07, *Luke Davies* <luke.davies_at_hansard.com
> <mailto:luke.davies_at_hansard.com>> wrote:
>
> Luc
>
> We did this same upgrade some time ago and what we did was alter
> all the varchar2 fields from BYTE to CHAR which then did not
> involve an increase in the size field (although, of course, may
> actually increase the storage of the column).
>
> After running csscan to identify truncated or lossy columns - we
> then exported those tables and then after changing the character
> set and modifying the columns, deleting the data (truncating)
> (which involved turning off foreign keys) and then importing the
> data back in.
>
> All went quite smoothly in the end after a few practice runs!
>
> HTH
> Luke
>
>
> Luc Demanche wrote:
>> Nigel,
>>
>> If I understand correctly, I only have to change the existing
>> column size ? Should I multiple by 4 the size of my varchar2 ?
>> Even if the column is not mentionned in the report of csscan ?
>>
>> After that, I recompile every storedprocs, views, etc manually.
>>
>> Then, I set the NLS_LENGTH_SEMANTICS=CHAR, so I don't have to
>> worry about the size of my varchar2 anymore ?
>>
>> Thank you
>> Luc
>>
>>
>> On 1/10/07, *Nigel Thomas* <nigel_cl_thomas_at_yahoo.com
>> <mailto:nigel_cl_thomas_at_yahoo.com>> wrote:
>>
>> Luc
>>
>>
>> Q1/Q3: If you set the parameter NLS_LENGTH_SEMANTICS=CHAR
>> then any ambiguous *new* column/variable definitions will be
>> made long enough for characters rather than bytes. That seems
>> a lot easier than changing every single table and package
>> definition.
>>
>> But existing columns won't be affected, as I recall. You
>> would need to MODIFY table/column definitions according (and
>> then recompile affected views, dependent packages etc).
>>
>> You should beware of the possible implications on index key
>> sizes (as the
>>
>> VARCHAR2 / NVARCHAR2 declarations in PL/SQL will be fixed as
>> the packages are recompiled (mostly this will happen
>> implicitly because of your DDL on the underlying tables - but
>> you should check that any packages that aren't automatically
>> recompiled are manually recompiled.
>>
>> Q2: of course Oracle limits SQL types (NOT in PL/SQL) to 4000
>> bytes - so up to 1000 * 4 byte chars (of course, most of your
>> characters will occupy just 1 or 2 bytes - your exact mileage
>> will vary depending on language). You can use CLOB instead,
>> and many string functions work directly against 'small' CLOBS
>> - but remember that CLOBs also have some drawbacks (LOB space
>> management etc), so only convert if you are sure you have to.
>>
>> HTH
>>
>> Regards Nigel
>>
>>
>>
>>
>>
>> --
>> Luc Demanche
>> Oracle DBA
>> (514) 867-9977
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> --
> Luc Demanche
> Oracle DBA
> (514) 867-9977

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